1. Field
This disclosure relates to gearless torque drives for torque-limiting devices that are suitable for operation at high rotational speeds.
2. General Background
Torque is a measure of force acting on an object that causes that object to rotate. In the case of a driver and a fastener, this measurement can be calculated mathematically in terms of the cross product of specific vectors:τ=r×F 
Where r is the vector representing the distance and direction from an axis of a fastener to a point where the force is applied and F is the force vector acting on the driver.
Torque has dimensions of force times distance and the SI unit of torque is the Newton meter (N-m). The joule, which is the SI unit for energy or work, is also defined as an N-m, but this unit is not used for torque. Since energy can be thought of as the result of force times distance, energy is always a scalar whereas torque is force cross-distance and so is a vector-valued quantity. Other non-SI units of torque include pound-force-feet, foot-pounds-force, ounce-force-inches, meter-kilograms-force, inch-ounces or inch-pounds.
Torque-limiting drivers are widely used throughout the medical industry. These torque-limiting drivers have a factory pre-set torque to ensure the accuracy and toughness required to meet a demanding surgical environment.
The medical industry has made use of both reusable and disposable torque-limiting drivers. In a surgical context, there is little room for error and these drivers must impart a precise amount of torque.
Reusable drivers require constant recalibration to ensure that the driver is imparting the precise amount of torque. Recalibration is a cumbersome task but must be done routinely. Such reusable devices also require sterilization.
Disposable drivers are an alternative to the reusable drivers. Once the driver has been used, it is discarded.
Disposable drivers are traditionally used for low torque applications. The standard torque values in these applications typically range from about 4 to about 20 inch-ounces. It has, however, been a challenge to develop a reliable disposable driver capable of imparting higher torques for larger applications.
Power tools are used for some applications in the medical industry. Such power tools can provide torque to a workpiece while also providing higher rotational rates than can be provided with manually driven tools. Torque-limiting systems can be utilized with medical power tools, either as an additional attachment provided in-line between the power tool and the workpiece or as internalized systems within the power tool itself. Reusable torque-limiting systems need to be sterilized between uses and typically must be serviced and recalibrated periodically to ensure performance within specifications. Disposable torque-limiting systems are an alternative to the reusable systems. Once the torque-limiting system has been used, it is discarded.
Disposable torque limiting devices which are inexpensive for use with power tools can fall out of specification with increased RPMs and as such fail to perform sufficiently.
Thus there is a need for disposable torque-limiting systems that can be utilized with medical power tools to limit applied torque at higher rotational speeds and remain in specification over a predetermined number of actuations. The disclosure is directed to these and other important needs.